GHSA-6v7q-wjvx-w8wg

Summary

basic-ftp's CRLF injection protection (added in commit 2ecc8e2 for GHSA-chqc-8p9q-pq6q) is incomplete. Two code paths bypass the protectWhitespace() control character check: (1) the login() method directly concatenates user-supplied credentials into USER/PASS FTP commands without any validation, and (2) the _openDir() method sends an MKD command before cd() invokes protectWhitespace(), creating a TOCTOU bypass. Both vectors allow an attacker who controls input to inject arbitrary FTP commands into the control connection.

Details

Vector 1: Credential Injection (login)

The login() method constructs FTP commands by direct string concatenation with no CRLF validation:

// src/Client.ts:216-231
login(user = "anonymous", password = "guest"): Promise<FTPResponse> {
    this.ftp.log(`Login security: ${describeTLS(this.ftp.socket)}`)
    return this.ftp.handle("USER " + user, (res, task) => {  // Line 218: no validation on `user`
        // ...
        else if (res.code === 331) {
            this.ftp.send("PASS " + password)  // Line 226: no validation on `password`
        }
    })
}

FtpContext.send() writes directly to the TCP socket:

// src/FtpContext.ts:223-227
send(command: string) {
    // ...
    this._socket.write(command + "\r\n", this.encoding)
}

The protectWhitespace() method (line 762) rejects \r, \n, and \0 characters — but it is only called for path-based operations. Credentials never pass through it.

The public access() method (line 268) passes options.user and options.password directly to login() with no sanitization.

Vector 2: MKD TOCTOU Bypass (_openDir)

The _openDir() method sends an MKD command before the CRLF check in cd():

// src/Client.ts:745-748
protected async _openDir(dirName: string) {
    await this.sendIgnoringError("MKD " + dirName)  // Line 746: sent BEFORE validation
    await this.cd(dirName)                           // Line...